My experience with NEC's tech support is that they are very responsive. I recommend you get in touch with them and ask them for advice.
DDC compliance is a difficult area, but it should work with NEC's own software. That said, you may wish to download a demo of BasicColor Display, install it and see whether using that program allows DDC to be recognized and operated. Before doing this, make sure your OS is reset to its default conditions in the graphics area and make sure you have correctly loaded the latest drivers for your video card. I would recommend using the DVI to DVI connection directly from the video card to the monitor, and pluf your colorimeter into a USB Port which is on the computer itself, hence directly connected to the motherboard. When you set-up BasicColor, make sure it is set to LUT V4 profile generation, that the correct colorimeter is selected, and the operation mode is set to allow the program to recognize DDC. Read the Manual before starting.